Block copolymer and composition thereof

ABSTRACT

The present invention provides a block copolymer or a hydrogenated product thereof excellent in low-temperature shrinkability, natural shrinkability, rigidity and the like, excellent in a balance of physical properties such as blocking resistance, resistance to fusion bonding in hot water, impact resistance and the like, and having a few fish eyes (FE&#39;s) caused by gels. Further, the invention provides a heat shrinkable film and a heat shrinkable multilayer film suitable for drink container packaging, cap seals and the like, using such a block copolymer or the hydrogenated product thereof. The invention provides a block copolymer having a weight ratio of a vinyl aromatic hydrocarbon and a conjugated diene of 60/40 to 90/10 and a number average molecular weight measured by gel permeation chromatography (GPC) of 30,000 to 500,000, wherein the vinyl aromatic hydrocarbon constituting the block copolymer has a block rate of from 10 to 90% by weight, the vinyl aromatic hydrocarbon polymer blocks constituting the block copolymer have a peak molecular weight within the molecular weight range of 5,000 to 30,000, and 40 to 80% by weight of the vinyl aromatic hydrocarbon polymer blocks have a molecular weight of 35,000 or less.

TECHNICAL FIELD

The present invention relates to a block copolymer suitable for a heatshrinkable film, which is excellent in a balance of physical propertiessuch as natural shrinkability, low-temperature shrinkability, rigidity,transparency and impact resistance, and a composition thereof.

Further, the invention relates to a sheet/film, a heat shrinkable filmand a heat shrinkable multilayer film which are excellent in a balanceof physical properties such as low-temperature shrinkability, naturalshrinkability, rigidity, blocking resistance, resistance to fusionbonding in hot water and impact resistance, and have a few fish eyes(FE's) caused by gels.

BACKGROUND ART

A block copolymer comprising a vinyl aromatic hydrocarbon and aconjugated diene, which has a relatively high vinyl aromatic hydrocarboncontent, has been used for injection molding applications and extrusionmolding applications such as sheets and films, utilizing characteristicssuch as transparency and impact resistance. In particular, a heatshrinkable film using the block copolymer comprising a vinyl aromatichydrocarbon and a conjugated diene has no problems of a residualmonomer, plasticizer residues and the generation of hydrogen chloride inburning of a vinyl chloride resin which has conventionally used, so thatit has been utilized for food packaging, cap seals, labels and the like.As characteristics necessary for a heat shrinkable film, there arerequirements such as natural shrinkability, low-temperatureshrinkability, transparency, mechanical strength and aptitude forpackaging machinery. In order to improve these characteristics andobtain a good balance of physical properties, various studies havehitherto been made.

For example, the document 1 identified below discloses a method forproducing a heat shrinkable film by preheating a styrene-butadiene blockcopolymer, and then, stretching it, in order to improve heatshrinkability. The document 2 identified below discloses a compositionof a vinyl aromatic hydrocarbon-aliphatic unsaturated carboxylic acidderivative copolymer having an aliphatic unsaturated carboxylic acidderivative content of 5 to 80% by weight and a Vicat softening point notexceeding 90° C., and a block copolymer comprising a vinyl aromatichydrocarbon and a conjugated diene, in order to obtain a compositionexcellent in mechanical characteristics, optical characteristics,stretching characteristics, crack resistance characteristics and thelike. The document 3 identified below discloses a heat shrinkable filmwhich comprises a block copolymer comprising a vinyl aromatichydrocarbon and a conjugated diene, the segments thereof having aspecific Tg, in order to obtain a heat shrinkable film excellent inshrinkable characteristics and environmental destruction resistance. Thedocument 4 identified below discloses a low-temperature shrinkable filmobtained by stretching a composition of a vinyl aromatichydrocarbon-aliphatic unsaturated carboxylic acid derivative copolymerhaving a vinyl aromatic hydrocarbon content of 95 to 20% by weight and aVicat softening point not exceeding 90° C., and a block copolymercomprising a vinyl aromatic hydrocarbon and a conjugated diene, in orderto obtain low-temperature shrinkability, optical characteristics, crackresistance characteristics, dimensional stability and the like. Thedocument 5 identified below discloses a polystyrene heat shrinkable filmcomprising a composition of a block copolymer comprising a styrene-basedhydrocarbon and a conjugated diene hydrocarbon and a styrene-basedhydrocarbon-containing random copolymer having a specific Tg, in orderto improve natural shrinkability at room temperature. The document 6identified below discloses a transparent high-strength resin compositioncontaining a block copolymer comprising a vinyl aromatic hydrocarbonblock of a specific structure and a copolymer block of a vinyl aromatichydrocarbon and a conjugated diene, and a copolymer of a vinyl aromatichydrocarbon and a (meth)acrylic ester, in order to obtain a resincomposition excellent in transparency and impact resistance. Thedocument 7 identified below discloses a multilayer low-temperatureshrinkable film having at least one layer of a composition of a vinylaromatic hydrocarbon-aliphatic unsaturated carboxylic acid derivativecopolymer having a vinyl aromatic hydrocarbon content of 95 to 20% byweight and a Vicat softening point not exceeding 90° C. and a blockcopolymer comprising a vinyl aromatic hydrocarbon and a conjugateddiene, in order to obtain a shrinkable film excellent in low-temperatureshrinkability, optical characteristics, crack resistancecharacteristics, dimensional stability and the like. The document 8identified below discloses a multilayer low-temperature shrinkablepolystyrene film having a specific heat shrinkage ratio in which anintermediate layer contains a styrene-(meth)acrylic ester copolymerhaving a specific Vicat softening point as a main component, and innerand outer layers have a styrene-conjugated diene block copolymer havinga specific Vicat softening point as a main component, in order to obtaina heat shrinkable film excellent in heat shrinkability at lowtemperatures, shrinkage finishing properties and natural shrinkageratio, and developing no blocking between films in a hot state.

However, these block copolymers comprising a vinyl aromatic hydrocarbonand a conjugated diene, or the compositions comprising the blockcopolymer and a vinyl aromatic hydrocarbon-aliphatic unsaturatedcarboxylic derivative copolymer are insufficient in a balance of naturalshrinkability, low-temperature shrinkability, rigidity, transparency,blocking resistance, resistance to fusion bonding in hot water andimpact resistance, and in inhibition of fish eyes (FE's) caused by gels.These documents do not disclose any methods for improving them.

[Patent Document 1]

-   -   JP 57-34921 A

[Patent Document 2]

-   -   JP 59-221348 A

[Patent Document 3]

-   -   JP 60-224520 A

[Patent Document 4]

-   -   JP 61-25919 A

[Patent Document 5]

-   -   JP 4-52129 A

[Patent Document 6]

-   -   JP 7-216187 A

[Patent Document 7]

-   -   JP 61-41544 A

[Patent Document 8]

-   -   JP 2002-46231 A

An object of the present invention is to provide a block copolymer and ahydrogenated product thereof, suitable for a heat shrinkable film, whichis excellent in a balance of physical properties such as naturalshrinkability, low-temperature shrinkability, rigidity, transparency andimpact resistance, and further to provide a composition thereof.Further, another object of the invention is to provide a sheet/film, aheat shrinkable film and a heat shrinkable multilayer film which areexcellent in a balance of blocking resistance and resistance to fusionbonding in hot water, in addition to the above-mentionedcharacteristics, and have a few FE's.

DISCLOSURE OF THE INVENTION

The present inventors have made extensive studies. As a result, it hasbeen found that the above-mentioned objects are achieved by a specificblock copolymer, thus completing the invention. That is, the inventionrelates to

-   -   a block copolymer having a weight ratio of a vinyl aromatic        hydrocarbon and a conjugated diene of 60/40 to 90/10 and a        number average molecular weight measured by gel permeation        chromatography (GPC) of 30,000 to 500,000,    -   wherein the vinyl aromatic hydrocarbon constituting the block        copolymer has a block rate of from 10 to 90% by weight, the        vinyl aromatic hydrocarbon polymer blocks constituting the block        copolymer have a peak molecular weight within the molecular        weight range of 5,000 to 30,000, and 40 to 80% by weight of the        vinyl aromatic hydrocarbon polymer blocks have a molecular        weight of 35,000 or less.

Further, the invention relates to a hydrogenated product of theabove-mentioned block copolymer, and a block copolymer compositioncomprising the above-mentioned block copolymer or the hydrogenatedproduct thereof.

Furthermore, the invention relates to a sheet/film, a heat shrinkablefilm and a heat shrinkable multilayer film which comprise theabove-mentioned block copolymer or the hydrogenated product thereof, orthe block copolymer composition.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described in detail below.

In the block copolymer of the invention, the weight ratio of the vinylaromatic hydrocarbon and the conjugated diene is from 60/40 to 90/10,preferably from 65/35 to 85/15, and more preferably from 70/30 to 83/17.When the ratio of the vinyl aromatic hydrocarbon and the conjugateddiene is 60/40 or more, rigidity is excellent, and when it is 90/10 orless, a heat shrinkable film improved in impact resistance can beobtained. The vinyl aromatic hydrocarbon content of the hydrogenatedproduct of the block copolymer may be grasped by the vinyl aromaticcompound content.

The block rate of the vinyl aromatic hydrocarbon incorporated into theblock copolymer of the invention is from 10 to 90% by weight, preferablyfrom 15 to 85% by weight, and more preferably from 25 to 80% by weight.When the block rate is 10% by weight or more, fusion bonding in hotwater is excellent, and when it is 85% by weight or less, a heatshrinkable film excellent in low-temperature shrinkability can beobtained. In the case of obtaining the block copolymer having goodrigidity, the block rate of the vinyl aromatic hydrocarbon isrecommended to be from exceeding 50% by weight to 90% by weight,preferably from 60 to 85% by weight, and more preferably from 65 to 80%by weight. In the invention, the vinyl aromatic hydrocarbon block meansone having an average polymerization degree of about 30 or more.

The block rate of the vinyl aromatic hydrocarbon incorporated into theblock copolymer of the invention can be measured by a method ofsubjecting the block copolymer before hydrogenation to oxidativedegradation using t-butyl hydroperoxide in the presence of osmiumtetraoxide as a catalyst (a method described in I. M. KOLTHOFF, et al.,J. Polym. Sci., 1, 429 (1946)), and means a value determined from thefollowing equation, using vinyl aromatic hydrocarbon polymer blockcomponents (provided that vinyl aromatic hydrocarbon polymer blockcomponents having an average polymerization degree of about 30 or lessare excluded) obtained by the method.Block rate (% by weight)=(the weight of the vinyl aromatic hydrocarbonpolymer blocks in the block copolymer/the weight of the whole vinylaromatic hydrocarbons in the block copolymer)×100

In the invention, for the purpose of obtaining a heat shrinkablemultilayer film excellent in balance performance of low-temperatureshrinkability and resistance to fusion bonding in hot water, the contentof the vinyl aromatic hydrocarbon polymer blocks in the block copolymeris recommended to be from exceeding 40% by weight to 85% by weight,preferably from 45 to 83% by weight, and more preferably from 50 to 80%by weight.

The vinyl aromatic hydrocarbon polymer blocks constituting the blockcopolymer of the invention have a peak molecular weight within themolecular weight range of 5000 to 30000, preferably 5000 to 20000, morepreferably 5000 to 15000, and particularly preferably 7000 to 13000.Particularly preferably, they have peak molecular weights within themolecular weight range of 5000 to 30000, preferably 5000 to 20000, morepreferably 5000 to 15000, and particularly preferably 7000 to 13000, andwithin the molecular weight range of 35000 to 150000, preferably 35000to 130000, more preferably 35000 to 100000 and particularly preferably40000 to 80000, respectively.

In the block copolymer of the invention, the vinyl aromatic hydrocarbonpolymer blocks have a peak molecular weight within the molecular weightrange of 5000 to 30000, thereby being able to obtain a heat shrinkablefilm excellent in natural shrinkability and low-temperatureshrinkability. Further, the vinyl aromatic hydrocarbon polymer blockshave peak molecular weights within the molecular weight range of 5000 to30000, and within the molecular weight range of 35000 to 150000,respectively, thereby being able to obtain a heat shrinkable filmexcellent in natural shrinkability, low-temperature shrinkability andresistance to fusion bonding in hot water.

In the block copolymer of the invention, 40 to 80% by weight, preferably45 to 80% by weight, more preferably 50 to 75% by weight andparticularly preferably 55 to 75% by weight of the vinyl aromatichydrocarbon polymer blocks incorporated into the block copolymer have amolecular weight of 35000 or less. When 40 to 80% by weight of the vinylaromatic hydrocarbon polymer blocks have a molecular weight of 35000 orless, a heat shrinkable film excellent in natural shrinkability andlow-temperature shrinkability can be obtained. In the invention, themolecular weight of the vinyl aromatic hydrocarbon polymer blocksincorporated into the block copolymer is specified by gel permeationchromatography (GPC) using the same vinyl aromatic hydrocarbon polymerblock components as those obtained by the above-mentioned oxidativedegradation method and used for the measurement of the block rate.Monodisperse polystyrene for gel permeation chromatography (GPC) issubjected to GPC to prepare calibration curves of the peak count numberthereof and the number average molecular weight of the monodispersepolystyrene, and the molecular weight is calculated according to aconventional method (for example, Gel Chromatography <Basic Course>,published by Kodansha Ltd.). The peak molecular weight can be determinedfrom a gel permeation chromatogram, and the ratio of the vinyl aromatichydrocarbon polymer block components having a molecular weight of 35000or less can be determined from the area ratio of the gel permeationchromatogram. The molecular weight of the vinyl aromatic hydrocarbonblocks incorporated into the block copolymer and the amount of thecomponents having a molecular weight of 35000 or less can be controlledby changing the weight of the vinyl aromatic hydrocarbon, the weights ofthe vinyl aromatic hydrocarbon and the conjugated diene and the weightratio thereof, the polymerization reactivity ratio, the amount of acatalyst and the like.

The block copolymer of the invention has a number average molecularweight (molecular weight in terms of polystyrene) measured by gelpermeation chromatography (GPC) ranging from 30000 to 500000, preferablyfrom 50000 to 500000 and more preferably from 70000 to 300000, and maybe a mixture of a plurality of block copolymers different in molecularweight. The preferred melt flow index (measured according to JIS K-6870,under conditions G, temperature: 200° C., load: 5 Kg) of the blockcopolymer is recommended to be from 0.1 to 100 g/10 min, from 0.5 to 50g/10 min, and more preferably from 1 to 30 g/10 min, in respect tomolding processability. The molecular weight and the melt flow index canbe arbitrarily adjusted by the amount of the catalyst used inpolymerization.

The block copolymer of the invention is preferably any of the followingblock copolymer mixtures:

-   -   (1) The block copolymer according to claim 1 or 2, which        comprises:    -   10 to 90 parts by weight of a block copolymer (component 1)        having a weight ratio of a vinyl aromatic hydrocarbon and a        conjugated diene constituting the block copolymer of from 70/30        to 95/5, wherein the vinyl aromatic hydrocarbon polymer blocks        have peak molecular weights within the molecular weight range of        5000 to 30000, and within the molecular weight range of 35000 to        150000, respectively; and    -   90 to 10 parts by weight of a block copolymer (component 2)        having a weight ratio of a vinyl aromatic hydrocarbon and a        conjugated diene constituting the block copolymer of from 50/50        to 85/15, wherein the vinyl aromatic hydrocarbon polymer blocks        have peak molecular weights within the molecular weight range of        5000 to 30000, and within the molecular weight range of 35000 to        150000, respectively,    -   with the proviso that the total amount of component 1 and        component 2 is 100 parts by weight, and that component 1 has a        vinyl aromatic hydrocarbon content larger than that of component        2 by at least 3% by weight;    -   (2) The block copolymer according to claim 1 or 2, which        comprises:    -   10 to 90 parts by weight of a block copolymer (component 1)        having a weight ratio of a vinyl aromatic hydrocarbon and a        conjugated diene constituting the block copolymer of from 70/30        to 95/5, wherein the vinyl aromatic hydrocarbon polymer blocks        have peak molecular weights within the molecular weight range of        5000 to 30000, and within the molecular weight range of 35000 to        150000, respectively; and    -   90 to 10 parts by weight of a block copolymer (component 3)        having a weight ratio of a vinyl aromatic hydrocarbon and a        conjugated diene constituting the block copolymer of from 50/50        to 85/15, wherein the vinyl aromatic hydrocarbon polymer blocks        have a peak molecular weight within the molecular weight range        of 5000 to 30000,    -   with the proviso that the total amount of component 1 and        component 3 is 100 parts by weight, and that component 1 has a        vinyl aromatic hydrocarbon content larger than that of component        3 by at least 3% by weight; and    -   (3) The block copolymer according to claim 1 or 2, which        comprises:    -   10 to 90 parts by weight of a block copolymer (component 4)        having a weight ratio of a vinyl aromatic hydrocarbon and a        conjugated diene constituting the block copolymer of from 70/30        to 95/5, wherein the vinyl aromatic hydrocarbon polymer blocks        have a peak molecular weight within the molecular weight range        of 5000 to 30000; and    -   90 to 10 parts by weight of a block copolymer (component 2)        having a weight ratio of a vinyl aromatic hydrocarbon and a        conjugated diene constituting the block copolymer of from 50/50        to 85/15, wherein the vinyl aromatic hydrocarbon polymer blocks        have peak molecular weights within the molecular weight range of        5000 to 30000, and within the molecular weight range of 35000 to        150000, respectively,    -   with the proviso that the total amount of component 4 and        component 2 is 100 parts by weight, and that component 4 has a        vinyl aromatic hydrocarbon content larger than that of component        2 by at least 3% by weight.

When the block copolymer of the invention is a block copolymer mixtureand, among combined mixtures of the above-mentioned components 1 to 4,in the case of a mixture of component 1 and component 2, component 1 isfrom 10 to 90% by weight, preferably from 15 to 85% by weight, and morepreferably from 20 to 80% by weight, and component 2 is from 90 to 10%by weight, preferably from 85 to 15% by weight, and more preferably from80 to 20% by weight (with the proviso that the total amount of component1 and component 2 is 100% by weight). In the invention, the vinylaromatic hydrocarbon content of component 1 is larger than that ofcomponent 2 by at least 3% by weight, preferably at least 5% by weight,more preferably at least 10% by weight.

When the block copolymer of the invention comprises a mixture ofcomponent 1 and component 3, component 1 is from 10 to 90% by weight,preferably from 15 to 85% by weight, and more preferably from 20 to 80%by weight, and component 3 is from 90 to 10% by weight, preferably from85 to 15% by weight, and more preferably from 80 to 20% by weight (withthe proviso that the total amount of component 1 and component 3 is 100%by weight). In the invention, the vinyl aromatic hydrocarbon content ofcomponent 1 is larger than that of component 3 by at least 3% by weight,preferably at least 5% by weight, more preferably at least 10% byweight.

When the block copolymer of the invention comprises a mixture ofcomponent 4 and component 2, component 4 is from 10 to 90% by weight,preferably from 15 to 85% by weight, and more preferably from 20 to 80%by weight, and component 2 is from 90 to 10% by weight, preferably from85 to 15% by weight, and more preferably from 80 to 20% by weight (withthe proviso that the total amount of component 4 and component 2 is 100%by weight). In the invention, the vinyl aromatic hydrocarbon content ofcomponent 4 is larger than that of component 2 by at least 3% by weight,preferably at least 5% by weight, more preferably at least 10% byweight. When the composition ratio of the respective components of themixture and the difference in the vinyl aromatic hydrocarbon content arewithin these ranges, a heat shrinkable film excellent in rigidity andimpact resistance can be obtained.

The content of short-chain vinyl aromatic hydrocarbon polymer moietieswith a vinyl aromatic hydrocarbon unit number of 1 to 3, based on thetotal amount of the vinyl aromatic hydrocarbons constituting the blockcopolymer of the invention is recommended to be from 1 to 25% by weight,preferably from 3 to 23% by weight, and more preferably from 5 to 20% byweight. When the content of the short-chain vinyl hydrocarbon polymermoieties is within the range of 1 to 25% by weight, rigidity is high andnatural shrinkability is good. The content of the short-chain vinylaromatic hydrocarbon polymer moieties can be determined by conductinggel permeation chromatography (GPC) of the vinyl aromatic hydrocarboncomponents, which has been obtained by dissolving the block copolymer indichloromethane, subjecting it to oxidative degradation with ozone (O₃),and then, reducing the resulting ozonide with lithium aluminum hydridein diethyl ether, followed by hydrolysis with pure water, andcalculating the area ratio of peaks obtained (see Takayuki Tanaka,Toshiya Sato and Yasunobu Nakafutami, Kobunshi Gakkai Yokoshu (Preprintsof Meeting of the Society of Polymer Science), 29, 2051 (1980)).

The content of the short-chain vinyl aromatic hydrocarbon polymermoieties can be controlled by changing the weights, the weight ratio,the polymerization reactivity ratio and the like of the vinyl aromatichydrocarbon and the conjugated diene in the course of copolymerizationof the vinyl aromatic hydrocarbon and the conjugated diene in theproduction of the block copolymer. As specific methods, there can beemployed methods of continuously supplying a mixture of the vinylaromatic hydrocarbon and the conjugated diene to a polymerization systemto polymerizing them, and/or copolymerizing the vinyl aromatichydrocarbon and the conjugated diene using a polar compound or arandomizing agent, and the like. The polar compounds and randomizingagents include an ether such as tetrahydrofuran, diethylene glycoldimethyl ether or diethylene glycol dibutyl ether, an amine such astriethylamine or tetramethylethylenediamine, a thioether, a phosphine, aphosphoramide, an alkylbenzenesulfonate, an alkoxide of potassium orsodium, and the like. The microstructure of conjugated diene monomerunits in the block copolymer, which is described later, can be adjustedby adding the polar compound or the like in a specified amount.

The block copolymer of the invention (including the above-mentionedblock copolymer components 1 to 4) has at least one segment constitutedby a vinyl aromatic hydrocarbon homopolymer and/or the copolymercomprising the vinyl aromatic hydrocarbon and the conjugated diene, andat least one segment constituted by a conjugated diene homopolymerand/or the copolymer comprising the vinyl aromatic hydrocarbon and theconjugated diene. Although there is no particular limitation on thepolymer structure of the block copolymer, there can be used, forexample, a linear block copolymer or a radial block copolymerrepresented by each of the following general formulas, or an arbitrarymixture of these polymer structures.(A-B)_(n),A-(B-A)_(n),B-(A-B)_(n+1),[(A-B)_(k)]_(m+1)-X,[(A-B)_(k)-A]_(m+1)-X,[(B-A)_(k)]_(m+1)-X and[(B-A)_(k)-B]_(m+1)-X(In the above formulas, segment A is the vinyl aromatic hydrocarbonhomopolymer and/or the copolymer comprising the vinyl aromatichydrocarbon and the conjugated diene, and segment B is the conjugateddiene homopolymer and/or the copolymer comprising the vinyl aromatichydrocarbon and the conjugated diene. X represents, for example, aresidue of a coupling agent such as silicon tetrachloride, tintetrachloride, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane or epoxidizedsoybean oil, or a residue of a polymerization initiator such as amultifunctional organic lithium compound. n, k and m are an integer of 1or more, generally an integer of 1 to 5. Further, the structures of aplurality of polymer chains bonded to X may be the same or different.)Furthermore, in the radial block copolymer represented by theabove-mentioned general formula, at least one A and/or B may be furtherbonded to X.

As for the relationship between the vinyl aromatic hydrocarbon contentin segment A ({the vinyl aromatic hydrocarbon in segment A/(the vinylaromatic hydrocarbon+the conjugated diene in segment A)}×100) and thevinyl aromatic hydrocarbon content in segment B ({the vinyl aromatichydrocarbon in segment B/(the vinyl aromatic hydrocarbon+the conjugateddiene in segment B)}×100), the vinyl aromatic hydrocarbon content insegment A is larger than the vinyl aromatic hydrocarbon content insegment B. The preferred difference in the vinyl aromatic hydrocarboncontent between segment A and segment B is preferably 5% by weight ormore. In the invention, the vinyl aromatic hydrocarbon in the copolymerof the vinyl aromatic hydrocarbon and the conjugated diene in segment Aand segment B may be distributed either uniformly or in a tapering(gradually decreasing) manner. Further, in the copolymer, a plurality ofmoieties in which the vinyl aromatic hydrocarbon is uniformlydistributed and/or a plurality of moieties in which the vinyl aromatichydrocarbon is distributed in a tapering manner may coexist in thesegment.

In the invention, the block copolymer before hydrogenation can beobtained by polymerizing the vinyl aromatic hydrocarbon and theconjugated diene in a hydrocarbon solvent, using an organic lithiumcompound as an initiator.

The vinyl aromatic hydrocarbons used in the invention include styrene,o-methylstyrene, p-methylstyrene, p-tert-butylstyrene,1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene,1,1-diphenylethylene, N,N-dimethyl-p-aminoethylstyrene,N,N-diethyl-p-aminoethylstyrene and the like, and particularly generalones include styrene. These may be used not only alone, but also as amixture of two or more thereof.

The conjugated diene is a diolefin having a pair of conjugated doublebonds, and examples thereof include 1,3-butadiene,2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene,1,3-pentadiene, 1,3-hexadiene and the like. Particularly general onesinclude 1,3-butadiene, isoprene and the like. These may be used not onlyalone, but also as a mixture of two or more thereof.

In the block copolymer of the invention, it is preferred that at leastone polymer block selected from the group consisting of (i) a copolymerblock comprising isoprene and 1,3-butadiene, (ii) a copolymer blockcomprising isoprene and a vinyl aromatic hydrocarbon and (iii) acopolymer block comprising isoprene, 1,3-butadiene and a vinyl aromatichydrocarbon is incorporated. In the case of the copolymer having abutadiene/isoprene weight ratio of 3/97 to 90/10, preferably 5/95 to85/15, more preferably 10/90 to 80/20, a few gels are formed in heatshaping-processing and the like.

In the invention, the block copolymer before hydrogenation is obtained,for example, by anionic living polymerization in a hydrocarbon solventusing an organic alkali metal compound or the like as an initiator. Asthe hydrocarbon solvents, there can be used, for example, an aliphatichydrocarbon such as n-butane, isobutane, n-pentane, n-hexane, n-heptaneor n-octane, an alicyclic hydrocarbon such as cyclopentane,methylcyclopentane, cyclohexane, methylcyclohexane, cycloheptane ormethylcycloheptane, or an aromatic hydrocarbon such as benzene, toluene,xylene or ethylbenzene. These may be used not only alone, but also as amixture of two or more thereof.

Further, as the polymerization initiator, there can be used an aliphatichydrocarbon alkali metal compound, an aromatic hydrocarbon alkali metalcompound, an organic aminoalkali metal compound or the like, which aregenerally known to have anionic polymerization activity to theconjugated diene and the vinyl aromatic compound. The alkali metalsinclude lithium, sodium, potassium and the like, and preferred examplesof the organic alkali metal compounds include an aliphatic and aromatichydrocarbon lithium compounds having 1 to 20 carbon atoms, a compoundcontaining one lithium atom in one molecule and a dilithium, trilithiumand tetralithium compounds containing a plurality of lithium atoms inone molecule. Specifically, they include n-propyllithium,n-butyllithium, sec-butyllithium, tert-butyllithium,hexamethylenedilithium, butadienyldilithium, isoprenyldilithium, areaction product of diisopropenylbenzene and sec-butyllithium, further areaction product of divinylbenzene, sec-butyllithium and a small amountof 1,3-butadiene, and the like. Further, organic alkali metal compoundsdisclosed in U.S. Pat. No. 5,708,092, British Patent 2,241,239, U.S.Pat. No. 5,527,753 and the like can also be used. These may be used notonly alone, but also as a mixture of two or more thereof.

In the invention, the polymerization temperature in the production ofthe block copolymer is generally from −10° C. to 150° C., and preferablyfrom 40° C. to 120° C. The time required for polymerization is usually10 hours or less, and particularly suitably from 0.5 to 5 hours althoughit varies depending on the conditions. Further, it is desirable toreplace the atmosphere of the polymerization system with an inert gassuch as nitrogen gas or the like. The polymerization pressure is notparticularly limited, and a pressure enough for holding the monomers andsolvent in a liquid phase in the above-mentioned polymerizationtemperature range may be used. Furthermore, it is necessary to payattention so as not to allow impurities that inactivates the catalystand living polymer, such as water, oxygen, carbon dioxide, etc. to enterinto the polymerization system. The hydrogenated product of the blockcopolymer of the invention is obtained by hydrogenating the blockcopolymer before hydrogenation obtained above. A hydrogenation catalystis not particularly limited, and there is used (1) a support typeheterogeneous hydrogenation catalyst in which a metal such as Ni, Pt, Pdor Ru is supported on a carbon, silica, alumina, diatomaceous earth orthe like, (2) a so-called Ziegler type hydrogenation catalyst using anorganic acid salt of Ni, Co, Fe, Cr or the like or a transition metalsalt such as an acetylacetone salt and a reducing agent such as anorganoaluminum compound, or (3) a homogeneous hydrogenation catalyst ofa so-called organic metal complex such as an organic metal compound ofTi, Ru, Rh, Zr or the like. As the specific hydrogenation catalysts,there can be used hydrogenation catalysts described in JP 42-8704 B, JP43-6636 B, JP 63-4841 B, JP 1-37970 B, JP 1-53851 B and JP 2-9041 B. Thepreferred hydrogenation catalysts include a titanocene compound and/or amixture with a reducing organic metal compound.

As the titanocene compounds, there can be used compounds described in JP8-109219 A. Specific examples thereof include a compound having at leastone ligand having a (substituted) cyclopentadienyl skeleton, an indenylskeleton or a fluorenyl skeleton, such as biscyclopentadienyltitaniumdichloride or monopentamethylcyclopentadienyltitanium trichloride.Further, the reducing organic metal compounds include an organic alkalimetal compound such as an organolithium compound, an organomagnesiumcompound, an organoaluminum compound, an organoboric compound, anorganozinc compound or the like.

The hydrogenation reaction is generally conducted within the temperaturerange of 0 to 200° C., preferably 30 to 150° C. The pressure of hydrogenused in the hydrogenation reaction is recommended to be from 0.1 to 15MPa, preferably from 0.2 to 10 MPa, and more preferably from 0.3 to 7MPa. Further, the hydrogenation reaction time is usually from 3 minutesto 10 hours, and preferably from 10 minutes to 5 hours. For thehydrogenation reaction, any one of a batch process, a continuous processand a combination thereof can be used.

In the hydrogenated product of the block copolymer of the invention, thehydrogenation ratio of unsaturated double bonds based on the conjugateddiene can be arbitrarily selected depending on the purpose, and is notparticularly limited. In order to obtain the block copolymerhydrogenated product having good heat stability and weather resistance,it is recommended that exceeding 70%, preferably 75% or more, morepreferably 85% or more and particularly preferably 90% or more of theunsaturated double bonds based on the conjugated diene are hydrogenated.Further, in order to obtain the block copolymer hydrogenated producthaving good heat stability, it is preferred that the hydrogenation ratiois from 3 to 70% or from 5 to 65%, and particularly preferably from 10to 60%. Although there is no particular limitation on the hydrogenationratio of aromatic double bonds based on the vinyl aromatic hydrocarbonin the copolymer, it is preferred that the hydrogenation ratio is 50% orless, preferably 30% or less, and more preferably 20% or less. Thehydrogenation ratio can be known by means of a nuclear magneticresonance apparatus (NMR).

In the invention, the microstructure (the ratio of cis, trans and vinyl)of the conjugated diene moiety in the block copolymer or thehydrogenated product can be arbitrarily changed by the use of theabove-mentioned polar compound or the like, and there is no particularlimitation thereon. In general, the amount of vinyl bonds can be setwithin the range of 5 to 90%, preferably 10 to 80%, more preferably 15to 75%. In the invention, the amount of vinyl bonds is the total amountof 1,2-vinyl bonds and 3,4-vinyl bonds (provided that it is the amountof 1,2-vinyl bonds, when 1,3-butadiene is used as the conjugated diene).The amount of vinyl bonds can be grasped with a nuclear magneticresonance apparatus (NMR).

In the invention, in order to obtain the block copolymer hydrogenatedproduct particularly excellent in fusion bonding in hot water, preferredis a block copolymer hydrogenated product having a crystallization peakat 20° C. or higher, preferably 30° C. or higher, more preferably withinthe temperature range of 45 to 100° C., particularly preferably 50 to90° C., in a differential scanning calorimetry (DSC) chart of the blockcopolymer hydrogenated product. It is preferred that the heat quantityof crystallization peak is 3 J/g or more, preferably 6 J/g or more, andmore preferably 10 J/g or more. The block copolymer hydrogenated producthaving the crystallization peak can be obtained by setting the amount ofvinyl bonds of the block copolymer before hydrogenation to less than30%, preferably 8 to 25%, more preferably 10 to 25%, and particularlypreferably 12 to 20%. In particular, it is recommended that the blockcopolymer before hydrogenation is allowed to contain at least oneconjugated diene polymer segment having an amount of vinyl bonds of 8 to25%, preferably 10 to 20%, and more preferably 10 to 18%.

The block copolymer of the invention and the hydrogenated productthereof (hereinafter referred to as component (A)) can be used as ablock copolymer composition with the vinyl aromatic hydrocarbon polymer(hereinafter referred to as component (B)). The weight ratio ofcomponent (A) and component (B) is from 99.9/0.1 to 20/80, preferably99.7/0.3 to 25/75, and more preferably from 99/1 to 30/70. The blockcopolymer composition excellent in rigidity, blocking resistance andnatural shrinkability can be obtained by combining component (A) andcomponent (B) at such weight ratios. In the invention, as the vinylaromatic hydrocarbon polymer, there can be used at least one selectedfrom the following a) to c):

-   -   a) Styrene polymer,    -   b) Aliphatic unsaturated carboxylic acid ester-styrene        copolymer, and    -   c) Rubber-modified styrene polymer

The styrene polymer a) used in the invention is one obtained bypolymerizing styrene or a monomer copolymerizable therewith (providedthat b) is excluded). The monomers copolymerizable with styrene includeα-methylstyrene, acrylonitrile, maleic anhydride and the like. Thestyrene polymers include polystyrene, a styrene-α-methylstyrenecopolymer, an acrylonitrile-styrene copolymer, a styrene-maleicanhydride copolymer and the like. Particularly preferred examples of thestyrene polymers include polystyrene. As for the weight averagemolecular weight of these styrene polymers, polymers of 50000 to 500000can be generally used. These styrene polymers can be used either aloneor as a mixture of two or more thereof, and utilized as a rigidityimprover.

An aliphatic unsaturated carboxylic acid ester of the aliphaticunsaturated carboxylic acid ester-styrene copolymer b) used in theinvention is one selected from an ester of a C1 to C12, preferably C2 toC12 alcohol and acrylic acid, such as methyl acrylate, ethyl acrylate,propyl acrylate, butyl acrylate, pentyl acrylate or hexyl acrylate, anester of methacrylic acid, a C1 to C12, preferably C2 to C12 alcohol andacrylic acid, and mono- or diester of an α- or β-unsaturateddicarboxylic acid such as fumaric acid, itaconic acid or maleic acid anda C1 to C12, preferably C2 to C12 alcohol. The content of the aliphaticunsaturated carboxylic acid ester in such an aliphatic unsaturatedcarboxylic acid ester-styrene copolymer is generally from 5 to 50% byweight, preferably from 8 to 30% by weight, and more preferably from 10to 25% by weight. Further, the Vicat softening point of the aliphaticunsaturated carboxylic acid ester-styrene copolymer is recommended to befrom 50 to 95° C., preferably from 60 to 90° C., and more preferablyfrom 65 to 85° C. The Vicat softening point is a value measured inaccordance with ASTM D-1525 (load: 1 Kg, temperature elevation rate: 2°C./min), using a compression molded product having a thickness of 3 mmas a test piece.

The preferred aliphatic unsaturated carboxylic acid ester-styrenecopolymer is a copolymer mainly comprising n-butyl acrylate and styrene,and an aliphatic unsaturated carboxylic acid ester-styrene copolymer inwhich the total amount of n-butyl acrylate and styrene is 50% by weightor more, and more preferably the total amount of n-butyl acrylate andstyrene is 60% by weight or more. A heat shrinkable film using thealiphatic unsaturated carboxylic acid ester-styrene copolymer mainlycomprising n-butyl acrylate and styrene has good shrinkability andnatural shrinkability.

In b), the above-mentioned vinyl aromatic hydrocarbon other than styrenemay be copolymerized within the range in which the characteristics ofthe invention are maintained. As a method for producing the aliphaticunsaturated carboxylic acid ester-styrene copolymer b), there can beused a known method for producing a styrene resin, for example, a bulkpolymerization method, a solution polymerization method, a suspensionpolymerization method, an emulsion polymerization method or the like. Asfor the weight average molecular weight of these aliphatic unsaturatedcarboxylic acid ester-styrene copolymers, polymers of 50000 to 500000can be generally used.

The rubber-modified styrene polymer c) used in the invention is obtainedby polymerizing a mixture of a monomer copolymerizable with the vinylaromatic hydrocarbon and an elastomer, and as a polymerization method,there has been generally conducted suspension polymerization, emulsionpolymerization, bulk polymerization, bulk-suspension polymerization orthe like. The monomers copolymerizable with the vinyl aromatichydrocarbons include α-methylstyrene, acrylonitrile, an acrylate, amethacrylate, maleic anhydride and the like. Further, as thecopolymerizable elastomer, there is used natural rubber, syntheticisoprene rubber, butadiene rubber, styrene-butadiene rubber, highstyrene rubber or the like.

These elastomers are dissolved generally in an amount of 3 to 50 partsby weight per 100 parts by weight of the vinyl aromatic hydrocarbon orthe monomer copolymerizable therewith or made into a latex form, andsubjected to emulsion polymerization, bulk polymerization,bulk-suspension polymerization or the like. Particularly preferredexamples of the rubber-modified styrene polymers include animpact-resistant rubber-modified styrene polymer (HIPS). Therubber-modified styrene polymer can be utilized as an improver forrigidity, impact resistance and slipperiness. As for the weight averagemolecular weight of these rubber-modified styrene polymers, polymers of50000 to 500000 can be generally used. The amount of the rubber-modifiedstyrene polymer added is preferably from 0.1 to 10 parts by weight,taking into account the maintenance of transparency.

The vinyl aromatic hydrocarbon polymer used in the invention isrecommended to have an MFR (under conditions G, temperature: 200° C.,load: 5 Kg) from 0.1 to 100 g/10 min, preferably from 0.5 to 50 g/10min, and from 1 to 30 g/10 min, in respect to molding processability.

At least one selected from a fatty acid amide, a paraffin and ahydrocarbon resin, and a fatty acid is added as a lubricant to the blockcopolymer, hydrogenated product thereof and block copolymer compositionof the invention in an amount of 0.01 to 5 parts by weight, preferably0.05 to 4 parts by weight, more preferably 0.1 to 3 parts by weight, per100 parts by weight of the block copolymer or the hydrogenated blockcopolymer, thereby improving blocking resistance.

The fatty acid amides include stearoamide, oleyl.amide, erucyl.amide,behen.amide, a mono- or bisamide of a higher fatty acid,ethylenebis.stearoamide, stearyl.oleylamide, N-stearyl.erucamide and thelike. These can be used either alone or as a mixture of two or morethereof. The paraffins and hydrocarbon resins include paraffin wax,microcrystalline wax, fluid paraffin, paraffinic synthetic wax,polyethylene.wax, combined wax, montan wax, hydrocarbon wax, siliconeoil and the like. These can be used either alone or as a mixture of twoor more thereof.

The fatty acids include a saturated fatty acid, an unsaturated fattyacid, an N-substituted fatty acid and the like, that is, a saturatedfatty acid such as lauric acid, palmitic acid, stearic acid, behenicacid or hydroxystearic acid, an unsaturated fatty acid such as oleicacid, erucic acid or ricinolic acid, a substituted fatty acid such asN-stearylstearic acid, N-oleyloleic acid, N-stearyloleic acid,N-oleylstearic acid, N-stearylerucic acid, N-oleylpalmitic acid,methylolstearic acid or methylolbehenic acid, a saturated fatty acidsuch as methylenebisstearic acid, ethylenebiscapric acid,ethylenebislauric acid, ethylenebisstearic acid, ethylenebisisostearicacid, ethylenebishydroxystearic acid, ethylenebisbehenic acid,hexamethylenebishydroxystearic acid, N,N′-distearyladipic acid orN,N′-distearylsebacic acid, an unsubstituted fatty acid such asethylenebisoleic acid, hexamethylenebisoleic acid, N,N′-dioleyladipicacid or N,N′-dioleylsebacic acid, m-xylylenebisstearic acid,N,N′-distearylisophthalic acid and the like. These can be used eitheralone or as a mixture of two or more thereof.

At least one ultraviolet absorber and light stabilizer selected from abenzophenone-based ultraviolet absorber, a benzotriazole-basedultraviolet absorber and a hindered amine-based light stabilizer isadded as an ultraviolet absorber and a light stabilizer to the blockcopolymer, hydrogenated product thereof and block copolymer compositionof the invention in an amount of 0.05 to 3 parts by weight, preferably0.05 to 2.5 parts by weight, more preferably 0.1 to 2 parts by weight,per 100 parts by weight of the block copolymer or the hydrogenated blockcopolymer, thereby improving light resistance.

The benzophenone-based ultraviolet absorbers include2,4-dihydroxy.benzophenone, 2-hydroxy-4-methoxy.benzophenone,2-hydroxy-4-n-octoxy.benzophenone, 4-hydroxy-2-hydroxy.benzophenone,1,4-bis(4-benzoyl-3-hydroxyphenoxy)butane,1,6-bis(4-benzoyl-3-hydroxyphenoxy)hexane and the like.

The benzotriazole-based ultraviolet absorbers include2-(2′-hydroxy-5′-methyl-phenyl)benzotriazole,2-(2′-hydroxy-3′,5′-di-t-butyl-phenyl)benzotriazole,2-(2′-hydroxy-3′-t-butyl-5′-methyl-phenyl)-5-chloro.benzotriazole,2-(2′-hydroxy-3′,5′-di-t-butyl-phenyl)-5-chloro.benzotriazole,2-(2-hydroxy-4-octyloxyphenyl)-2H-benzotriazole,2-(2H-benzotriazole-2-yl)-4-methyl-6-(3,4,5,6-tetrahydro-phthalimidylmethyl)phenoland the like.

The hindered amine-based light stabilizers includebis(2,2,6,6-tetramethyl-4-piperidyl) sebacate,bis-(1,2,6,6,6,-pentamethyl-4-piperidyl)sebacate,1-[2-{3-(3,5-di-tertiarybutyl-4-hydroxyphenyl)propionyloxy}-ethyl]-4-{3-(3,5-di-tertiarybutyl-4-hydroxyphenyl)-propionyloxy}-2,2,6,6-tetramethylpiperidine,8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4,5]decane-2,4-dione,4-benzoyloxy-2,2,6,6-tetramethylpiperidine,poly[[6-1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[[2,2,6,6-tetramethyl-4-piperidyl]imino]],poly[6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetramethyl-4-piperidyl)imino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]],2-(3,5-di-tertiary butyl-4-hydroxybenzyl)-2-n-butylmalonic acidbis(1,2,2,6,6-pentamethyl-4-piperidyl) and the like.

2-[1-(2-Hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenylacrylate is added as a stabilizer to the block copolymer, hydrogenatedproduct thereof and block copolymer composition of the invention in anamount of 0.05 to 3 parts by weight, more preferably 0.1 to 2 parts byweight, per 100 parts by weight of the block copolymer or thehydrogenated block copolymer, thereby being able to obtain a gelinhibiting effect. When the stabilizer is less than 0.05 parts byweight, no gel inhibition effect is obtained, and addition exceeding 3parts by weight results in no contribution to the gel inhibition effecthigher than that of the invention.

At least one of phenolic stabilizers such asn-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methyl-phenylacrylate, 2,4-bis[(octylthio)methyl]-o-cresol,tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene and2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazinecan be added in an amount of 0.05 to 3 parts by weight per 100 parts byweight of the block copolymer, and at least one of organic phosphate-and organic phosphite-based stabilizers such astris-(nonylphenyl)phosphite, 2,2-methylenebis(4,6-di-t-butylphenyl)octylphosphite,2-[[2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosphepin-6-yl]oxy]-N,N-bis[2-[[2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosphepin-6-yl]oxy]ethyl]ethaneamineand tris(2,4-di-t-butylphenyl) phosphite can be added in an amount of0.05 to 3 parts by weight per 10 parts by weight of the block copolymeror the hydrogenated block copolymer.

Various polymers and additives can be added to the block copolymer,hydrogenated product thereof and block copolymer composition of theinvention depending on the purpose. Suitable examples of the polymersinclude a block copolymer elastomer of a vinyl aromatic hydrocarbon anda conjugated diene or a hydrogenated product thereof, a block copolymerresin of a vinyl aromatic hydrocarbon and a conjugated diene, differentfrom the block copolymer of the invention, and the like.

In the invention, as the block copolymer elastomer of a vinyl aromatichydrocarbon and a conjugated diene or the hydrogenated product thereof,there can be used one having a vinyl aromatic hydrocarbon content ofless than 60% by weight, preferably from 10 to 50% by weight, and havinga structure similar to that of the block copolymer of the invention. Itis blended in an amount of 0.5 to 30 parts by weight, preferably from 1to 20 parts by weight, per 100 parts by weight of the block copolymer ofthe invention, thereby being able to improve impact resistance,elongation and the like.

In the hydrogenated product of the block copolymer elastomer, thehydrogenation ratio of unsaturated double bonds based on the conjugateddiene can be arbitrarily selected depending on the purpose, and is notparticularly limited. 70% or more, preferably 80% or more, morepreferably 90% or more of the unsaturated double bonds based on theconjugated diene in the block copolymer elastomer may be hydrogenated,or only a part thereof may be hydrogenated. When only a part ishydrogenated, it is preferred that the hydrogenation ratio is adjustedto 10% to less than 70%, or 15% to less than 65%, and 20% to less than60% as needed.

As the block copolymer resin of a vinyl aromatic hydrocarbon and aconjugated diene, which is different from the block copolymer of theinvention or the hydrogenated product thereof, there can be used onehaving a vinyl aromatic hydrocarbon content of 60 to 95% by weight,preferably from 65 to 90% by weight, and having a structure similar tothat of the block copolymer of the invention. It is blended in an amountof 5 to 90 parts by weight, preferably from 10 to 80 parts by weight,per 100 parts by weight of the block copolymer of the invention, therebybeing able to improve impact resistance, rigidity, elongation and thelike.

The other suitable additives include a softening agent such as acoumarone-indene resin, a terpene resin or an oil, and a plasticizer.Further, various stabilizers, pigments, antiblocking agents, antistaticagents, lubricants and the like can also be added. As the blockingagent, the antistatic agent and the lubricant, there can be used, forexample, a fatty acid amide, ethylenebis(stearoamide), sorbitanmonostearate, a saturated fatty acid ester of a fatty acid alcohol, apentaerythritol fatty acid ester and the like, and as the ultravioletabsorber, there can be used compounds described in Practical Handbook ofAdditives for Plastics and Rubbers (Kagaku Kogyosha), such asp-t-butylphenyl salicylate, 2-(2′-hydroxy-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole and2,5-bis-[5′-t-butylbenzoxazolyl-(2)]thiophene. These are used generallywithin the range of 0.01 to 5% by weight, preferably within the range of0.05 to 3% by weight.

The block copolymer of the invention, the hydrogenated product thereof,or the block copolymer composition comprising the block copolymer andthe vinyl aromatic hydrocarbon polymer can be used as various formingmaterials and the like for sheets, films, injection molded products andthe like.

A heat shrinkable uniaxially or biaxially stretched film using the blockcopolymer of the invention, the hydrogenated product thereof, or theblock copolymer composition comprising the block copolymer and the vinylaromatic hydrocarbon polymer can be obtained by extrusion molding theblock copolymer through an ordinary T-die or circular die in a flat ortube form at 150 to 250° C., preferably 170 to 220° C., andsubstantially uniaxially or biaxially stretching the resultingunstretched product.

For example, in uniaxial stretching, stretching is carried out in anextrusion direction with a calender roll or the like, in the case of afilm form or a sheet form, or in a rectangular direction to theextrusion direction with a tenter or the like. In the case of a tubeform, stretching is carried out in an extrusion direction orcircumferential direction of a tube. In biaxial stretching, an extrudedfilm or sheet is longitudinally stretched with a metal roll or the like,and then laterally stretched with a tenter or the like, in the case of afilm form or a sheet form. In the case of a tube form, stretching iscarried out in an extrusion direction of a tube and in a circumferentialdirection of a tube, that is, in rectangular directions to a tube axis,at the same time or separately.

In the invention, it is preferred that stretching is carried out at astretching temperature of 60 to 110° C., preferably 80 to 100° C.,longitudinally and/or laterally at a stretching ratio of 1.5 to 8,preferably 2 to 6. When the stretching temperature is less than 60° C.,breakage occurs to cause the difficulty to obtain a desired heatshrinkable film. Exceeding 110° C. results in the difficulty to obtain afilm having good shrinkage characteristics. The stretching ratio isselected within the above-mentioned range so as to correspond to therequired shrinkage ratio depending on the application. However, when thestretching ratio is less than 1.5, the heat shrinkage ratio isunfavorably low for heat shrink packaging. Further, a stretching ratioexceeding 8 is unfavorable in respect to stable production in astretching processing process. In the case of biaxial stretching, thelongitudinal and lateral stretching ratios may be the same or different.Then, it is also possible that a heat shrinkable film uniaxially orbiaxially stretched is heat treated at 60 to 105° C., preferably at 80to 95° C., for a short period of time, for example, for 3 to 60 seconds,preferably 10 to 40 seconds, as needed, thereby conducting a means forpreventing natural shrinkage at room temperature.

In order to use the heat shrinkable film thus obtained as a material forheat shrink packaging or a material for a heat shrinkable label, theheat shrinkage ratio at 65° C. in a stretching direction is recommendedto be from 5 to 60%, preferably from 10 to 55%, and more preferably from15 to 50%. When the heat shrinkage ratio is within such a range, a heatshrinkable film excellent in a balance between the heat shrinkage ratioand the natural shrinkage ratio is obtained. In the invention, the heatshrinkage ratio at 65° C. is a measure of low-temperature shrinkability,and the heat shrinkage ratio in each stretching direction of a formedarticle at the time when the uniaxially or biaxially stretched film isimmersed in a heat medium not inhibiting the characteristics of theformed article, such as hot water, silicone oil, glycerol or the like at65° C. for 5 minutes. In the invention, within the above-mentioned rangeof the heat shrinkage ratio, the natural shrinkage ratio of the heatshrinkable film itself is recommended to be 2.5% or less, preferably2.0% or less, and more preferably 1.5% or less. The natural shrinkageratio of the heat shrinkable film itself as used herein means a valueobtained by allowing the heat shrinkable film within the above-mentionedrange of heat shrinkage to stand at 35° C. for 5 hours, and calculatingby an equation described later.

Further, in the uniaxially or biaxially stretched film of the invention,it is necessary as a heat shrink packaging material that the tensileelastic modulus in the stretching direction is from 7000 to 30000Kg/cm², and preferably from 10000 to 25000 Kg/cm². When the tensileelastic modulus in the stretching direction is less than 7000 Kg/cm²,settling occurs in a shrink packaging process to unfavorably causeabnormal packaging. Exceeding 30000 Kg/cm² is unfavorable because theimpact resistance of the film decreases.

When the uniaxially or biaxially stretched film of the invention is usedas the heat shrinkable packaging material, it can be heat shrunk byheating at a temperature of 130 to 300° C., preferably 150 to 250° C.,for several seconds to several minutes, preferably 1 to 60 seconds.

The heat shrinkable film of the invention may be a multilayer laminatehaving at least two-layer, preferably at least three-layer structure.Specific examples of types of usage as the multilayer laminates include,for example, types disclosed in JP 3-5306 B. The block copolymer,hydrogenated block copolymer or block copolymer composition of theinvention may be used in an intermediate layer or both outer layers.When the block copolymer, hydrogenated product thereof or blockcopolymer composition of the invention are used in the multilayer film,there is no particular limitation on a layer other than the film layerusing the block copolymer, hydrogenated product thereof or blockcopolymer composition of the invention. It may be a layer comprising theblock copolymer, hydrogenated product thereof or block copolymercomposition of the invention different in constituting components,composition or the like, or a layer in which a block copolymer otherthan the invention is combined with a composition of a block copolymerother than the invention and the above-mentioned vinyl aromatichydrocarbon polymer. In addition, there is mentioned at least onecomponent selected from polypropylene, polyethylene, an ethylenicpolymer (an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylatecopolymer, an ethylene-acrylic acid copolymer or the like), an ionomerresin, a nylon-based resin, a polyester-based resin, a polymethylmethacrylate resin, an ABS resin, the above-mentioned vinyl aromatichydrocarbon polymer and the like. However, preferred is the blockcopolymer other than the invention or the composition of the blockcopolymer other than the invention and the above-mentioned vinylaromatic hydrocarbon polymer, or the above-mentioned vinyl aromatichydrocarbon polymer.

In the invention, the preferred heat shrinkable multilayer film is aheat shrinkable multilayer film having a layer comprising the blockcopolymer, hydrogenated product thereof or block copolymer compositionof the invention as at least one layer of the multilayer film, whereinthe heat shrinkage ratio at 80° C. in the stretching direction is from10 to 80%, preferably from 15 to 70%, and more preferably from 20 to60%. The block copolymer or the hydrogenated product thereof used insuch a heat shrinkable multilayer film is preferably a block copolymeror a hydrogenated product thereof which satisfies the requirementsspecified in the invention, has at least two peaks within the molecularweight (molecular weight in terms of polystyrene) range of 40000 to300000, preferably 45000 to 280000, more preferably 50000 to 280000, inthe gel permeation chromatography (GPC) measurement, and has at leastone tan δ peak temperature within the temperature range of 90 to 125°C., preferably 92 to 123° C., more preferably 95 to 120° C., in thedynamic viscoelasticity measurement, thereby obtaining the heatshrinkable multilayer film excellent in natural shrinkability andresistance to fusion bonding in hot water.

In the invention, function tan δ in the dynamic viscoelasticitymeasurement is a value measured with a viscoelasticity measuringanalyzer, DVE-V4, manufactured by Rheology Co., Ltd., and is measuredunder the conditions of an oscillation frequency of 35 Hz and atemperature elevation rate of 3° C./min using a test piece having athickness of 0.5 to 2 mm. The temperature showing the peak means atemperature at which the primary differentiated value of the variationof the value of tan δ to the temperature becomes zero. The peaktemperature of tan δ is adjusted by the weight ratio of the vinylaromatic hydrocarbon and the conjugated diene, the molecular weight ofthe block copolymer, the content of the vinyl aromatic hydrocarbonpolymer blocks in the block copolymer, the content of short-chain vinylaromatic hydrocarbon polymer moieties with a vinyl aromatic hydrocarbonunit number of 1 to 3 in the block copolymer, etc.

The block copolymer of the invention or the hydrogenated product thereofsuitably available in the heat shrinkable multilayer film has at least 2peaks within the molecular weight range of 40000 to 300000, therebybeing excellent in a balance among physical properties such as rigidityand impact resistance. Such a block copolymer or the hydrogenatedproduct thereof can be obtained by mixing the block copolymers differentin the composition of the vinyl aromatic hydrocarbon and the conjugateddiene and the molecular weight, or conducting polymerization in the samereaction vessel, adjusting the molecular weight. As adjustment of themolecular weight in the same reaction vessel, there is a method ofadding an initiator more than once, a method of adding a multifunctionalcoupling agent to ends having polymerization activity, a method ofpartly inactivating active ends during polymerization, or the like. Whenthe active ends are partly inactivated during polymerization, a methodof adding an active hydrogen-containing compound such as an alcohol, aphenol compound, a carboxylic-acid, an amine compound or water, a ketonecompound or an epoxy compound is generally used.

As for the ratio of components which exist in the above-mentioned blockcopolymer or the hydrogenated product thereof suitably applicable in theheat shrinkable multilayer film and show at least two peaks, it ispreferred that the weight rate of a component showing the maximummolecular weight and other components is 10/90 to 90/10, preferably20/80 to 80/20, and more preferably 70/30 to 30/70. The weight rate ofthese can be grasped by the weight ratio of the respective componentsmixed when they are mixed, and can be grasped by polymerizationconditions thereof when they are polymerized in the same reactionvessel. Further, it can also be grasped from the area ratio of therespective components in a gel permeation chromatogram.

As the heat shrinkable multilayer film of the invention, there can alsobe obtained a heat shrinkable multilayer film in which the heatshrinkage ratio at 65° C. in the stretching direction is from 5 to 60%,preferably from 10 to 55%, and more preferably from 15 to 50%, and thetensile elastic modulus in the stretching direction is from 7000 to30000 Kg/cm², and preferably from 10000 to 25000 Kg/cm².

The thickness of the heat shrinkable film and heat shrinkable multilayerfilm of the invention is from 10 to 300 μm, preferably from 20 to 200μm, and more preferably from 30 to 100 μm, and the thickness ratio of aninner layer and both surface layers is recommended to be from 5/95 to45/55, and preferably from 10/90 to 35/65.

The heat shrinkable film of the invention can be utilized for variousapplications, for example, packages of fresh food and confectionery,packages of clothes, writing materials and the like, and the like. Theparticularly preferred applications include utilization as a so-calledmaterial for a heat shrinkable label, in which letters or designs areprinted on the uniaxially stretched film of the block copolymerspecified in the invention, and then, the film is closely adhered byheat shrinkage to a surface of an article to be packaged, such as aplastic molded article, a metal product, a glass vessel or a porcelainto use.

In particular, the uniaxially stretched heat shrinkable film of theinvention is excellent in low-temperature shrinkability, rigidity andnatural shrinkability, so that it can be suitably utilized as a heatshrinkable label material for a material extremely different from theblock copolymer of the invention in the coefficient of thermalexpansion, water absorption properties or the like, for example, avessel using at least one selected from a metal, a ceramic, glass,paper, a polyolefinic resin such as polyethylene, polypropylene orpolybutene, a polymethacrylate resin, a polycarbonate resin, a polyesterresin such as polyethylene terephthalate or polybutylene terephthalateand a polyamide resin, as a constituent material, as well as the heatshrinkable label material for the plastic molded article so as to deformon heating at high temperatures.

The materials constituting plastic vessels for which the heat shrinkablefilm of the invention include polystyrene, rubber-modified high-impactpolystyrene (HIPS), a styrene-butyl acrylate copolymer, astyrene-acrylonitrile copolymer, a styrene-maleic anhydride copolymer,an acrylonitrile-butadiene-styrene copolymer (ABS), amethacrylate-butadiene-styrene copolymer (MBS), a polyvinyl chlorideresin, a polyvinyl chloride resin, a phenol resin, a urea resin, amelamine resin, an epoxy resin, an unsaturated polyester resin, asilicone resin and the like, as well as the above-mentioned resins.These plastic vessels may be either a mixture of two or more of theresins or a laminate.

When the heat shrinkable film of the invention is used as the materialfor a heat shrinkable label, the heat shrinkage ratio at 65° C. in arectangular direction to the stretching direction is less than 20%, andpreferably 10% or less. Accordingly, the uniaxial stretching for theheat shrinkable label in the invention means to conduct stretchingtreatment so as to provide a heat shrinkage ratio at 65° C. in thestretching direction of 5 to 60% and a heat shrinkage ratio in arectangular direction to the stretching direction of less than 20%

EXAMPLES

Examples of the invention are described below, but these should not beconstrued as limiting the scope of the invention.

Table 1, Table 2, Table 5, Table 6 and Table 7 show block copolymers,Table 3 shows styrene-n-butyl acrylate copolymers and general-purposepolystyrene as vinyl aromatic hydrocarbon polymers, and Table 7 shows astyrene-n-butyl acrylate copolymer, a styrene-methyl methacrylatecopolymer, high-impact polystyrene (HIPS) and general-purposepolystyrene.

(Preparation of Block Copolymer A-1 to A-11)

Block copolymers having styrene contents (% by weight), block rates (%by weight) and block styrene molecular weights shown in Table 1 andTable 2 were produced in a cyclohexane solvent using n-butyllithium as acatalyst and tetramethylethylenediamine as a randomizing agent. Thestyrene content was adjusted by the amounts of styrene and butadiene(including isoprene when isoprene is contained) added, the block ratewas adjusted by the styrene contents of segment A and segment B, and themolecular weight of block styrene was adjusted by the styrene contentsof segment A and segment B and the content ratio. In the preparation ofthe block copolymer, monomers diluted with cyclohexane to aconcentration of 20% by weight were used.

As the hydrogenation catalyst, there was used a hydrogenation catalystobtained by putting 1 liter of dried purified cyclohexane in anitrogen-substituted reaction vessel, adding 100 mmol ofbis(η5-cyclopentadienyl)titanium dichloride, and adding an n-hexanesolution containing 200 mmol of trimethylaluminum with thoroughlystirring, followed by reaction at room temperature for about 3 days.

1) Block Copolymer A-1

Using an autoclave equipped with a stirrer, 0.049 part by weight ofn-butyllithium and 0.03 part by weight of tetramethylethylenediaminewere added to a cyclohexane solution containing 12.5 parts by weight of1,3-butadiene under an atmosphere of nitrogen gas, and polymerizationwas conducted at 75° C. for 15 minutes. Then, a cyclohexane solutioncontaining 13.2 parts by weight of styrene and 1.5 parts by weight of1,3-butadiene was continuously added for 10 minutes, and polymerizationwas conducted at 75° C., followed by keeping for 5 minutes. This processwas repeated 5 times. Then, methanol was added in an amount of 0.3 timethe molar quality of n-butyllithium, and then, a cyclohexane solutioncontaining 14 parts by weight of styrene was added, followed bypolymerization at 75° C. for 20 minutes. Thereafter, methanol was addedto a reaction device in an amount of 0.6 time the molar quality ofn-butyllithium to stop the polymerization, and2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenylacrylate was added as a stabilizer in an amount of 0.6 part by weightper 100 parts by weight of the block copolymer composition, followed bydesolvation to obtain a block copolymer.

2) Block Copolymers A-2 to A-5

Block copolymers A-2 to A-5 were prepared in a similar manner as withA-1.

3) Block Copolymer A-6

Block copolymer A-6 comprised two types of component 1 and component 2different in composition, and was produced as follows.

As for component 1, using an autoclave equipped with a stirrer, 0.041part by weight of n-butyllithium and 0.03 part by weight oftetramethylethylenediamine were added to a cyclohexane solutioncontaining 12 parts by weight of styrene under an atmosphere of nitrogengas, and polymerization was conducted at 75° C. for 20 minutes. Then, acyclohexane solution containing 50 parts by weight of styrene, 10 partsby weight of 1,3-butadiene and 15 parts by weight of isoprene wascontinuously added for 10 minutes, and polymerization was conducted at75° C., followed by keeping for 30 minutes. Then, a cyclohexane solutioncontaining 25 parts by weight of styrene was added, followed bypolymerization at 75° C. for 20 minutes. Thereafter, methanol was addedto a reaction device in an amount of 0.9 time the molar quality ofn-butyllithium to stop the polymerization.

As for component 2, using an autoclave equipped with a stirrer, 0.09part by weight of n-butyllithium and 0.02 part by weight oftetramethylethylenediamine were added to a cyclohexane solutioncontaining 8 parts by weight of styrene under an atmosphere of nitrogengas, and polymerization was conducted at 75° C. for 15 minutes. Then, acyclohexane solution containing 40 parts by weight of styrene, 12.8parts by weight of 1,3-butadiene and 19.2 parts by weight of isoprenewas continuously added for 5 minutes, followed by keeping at 75° C. for30 minutes. Then, a cyclohexane solution containing 20 parts by weightof styrene was added, followed by polymerization at 75° C. for 20minutes. Thereafter, methanol was added to a reaction device in anamount of 0.9 time the molar quality of n-butyllithium to stop thepolymerization.

Component 1 and component 2 were mixed at a weight ratio of 60/40, andthen, 2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenylacrylate was added as a stabilizer in an amount of 0.6 part by weightper 100 parts by weight of the block copolymer composition, followed bydesolvation to obtain block copolymer A-6.

4) Block Copolymers A-7 and A-8

Block copolymers A-7 and A-8 were prepared in a similar manner as withblock copolymer A-6.

5) Block Copolymer A-9

Using an autoclave equipped with a stirrer, 0.070 part by weight ofn-butyllithium and 0.03 part by weight of tetramethylethylenediaminewere added to a cyclohexane solution containing 15 parts by weight ofstyrene under an atmosphere of nitrogen gas, and polymerization wasconducted at 75° C. for 20 minutes. Then, a cyclohexane solutioncontaining 1 part by weight of 1,3-butadiene and 15 parts by weight ofstyrene was added for 1 minute, and polymerization was further conductedat 75° C. for 20 minutes. Then, a cyclohexane solution containing 20parts by weight of styrene, 14 parts by weight of 1,3-butadiene and 16parts by weight of isoprene was continuously added for 30 minutes, andpolymerization was conducted at 75° C. Then, a cyclohexane solutioncontaining 1 part of 1,3-butadiene and 18 parts by weight of styrene wascontinuously added at 75° C. for 20 minutes, and polymerization wasconducted. Thereafter, methanol was added to a reaction device in anamount of 0.9 time the molar quality of n-butyllithium to stop thepolymerization, and2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenylacrylate was added as a stabilizer in an amount of 0.6 part by weightper 100 parts by weight of the block copolymer composition, followed bydesolvation to obtain a block copolymer.

6) Block Copolymer A-10

Using an autoclave equipped with a stirrer, a cyclohexane solutioncontaining 20 parts by weight of styrene and 0.135 part by weight ofn-butyllithium based on 100 parts by weight of the total used monomerswere added under an atmosphere of nitrogen gas, and polymerization wasconducted at 75° C. for 30 minutes. Then, a cyclohexane solutioncontaining 15 parts by weight of 1,3-butadiene was added, andpolymerization was conducted at 75° C. for 30 minutes. Thereafter, acyclohexane solution containing 15 parts by weight of styrene was added,and polymerization was conducted at 75° C. for 30 minutes. Then, acyclohexane solution containing tetramethylethylenediamine in an amountof 0.2 time the molar quality of n-butyllithium previously added.Thereafter, a cyclohexane solution containing 20 parts of styrene and 10parts by weight of 1,3-butadiene was continuously added for 10 minutes,and polymerization was conducted at 75° C., followed by keeping for 30minutes. Then, methanol was added in an amount of 0.7 time the molarquality of n-butyllithium, and thereafter, a cyclohexane solutioncontaining 20 parts by weight of styrene was added, followed bypolymerization at 75° C. for 30 minutes.

Then, a hydrogenation catalyst was added to a solution of the blockcopolymer obtained above in an amount of 100 ppm as titanium based on100 parts by weight of the block copolymer, and hydrogenation reactionwas conducted under a hydrogen pressure of 0.7 MPa at a temperature of65° C. Thereafter, methanol was added, and then,octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate was added as astabilizer in an amount of 0.3 part by weight per 100 parts by weight ofthe block copolymer.

Characteristics of the resulting block copolymer A-10 are shown in Table5. The hydrogenation ratio of block copolymer A-10 was 98%, thecrystallization peak temperature was 60° C., and the heat quantity ofcrystallization peak was 16.5 J/g.

7) Block Copolymer A-11

A block copolymer mixture was obtained in the same manner as with blockcopolymer A-6 with the exception that the amounts of n-butyllithium usedin the preparation of component 1 and component 2 of block copolymer A-6were changed.

Then, a hydrogenation catalyst was added to a solution of the blockcopolymer mixture obtained above in an amount of 100 ppm as titaniumbased on 100 parts by weight of the block copolymer, and hydrogenationreaction was conducted under a hydrogen pressure of 0.7 MPa at atemperature of 65° C. Thereafter, methanol was added, and then,octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate was added as astabilizer in an amount of 0.3 part by weight per 100 parts by weight ofthe block copolymer.

Characteristics of the resulting block copolymer A-11 are shown in Table5. The hydrogenation ratio of block copolymer A-11 was adjusted by theamount of hydrogen so as to give a hydrogenation ratio of about 35%, andwas about 35%.

(Preparation of Block Copolymers C-1 to C-19 and D-1)

Block copolymers used in Examples which have at least one polymer blockmainly comprising a vinyl aromatic hydrocarbon, at least one polymerblock comprising a conjugated diene, and at least one polymer blockcomprising a conjugated diene and an vinyl aromatic hydrocarbon areshown in Table 5, Table 6 and Table 7. The block copolymers wereobtained by adding n-butyllithium as a polymerization initiator incyclohexane, adding tetramethylethylenediamine as a randomizing agentfor adjustment of the content of single-chain styrene as needed, andconducting polymerization. In the preparation of the block copolymers,monomers diluted with cyclohexane to a concentration of 20% by weightwere used.

8) Block Copolymer C-1

Block copolymer C-1 was produced in the following manner.

<Low Molecular Weight Block Copolymer Moiety>

Using an autoclave equipped with a stirrer, 0.088 part by weight ofn-butyllithium and 0.03 part by weight of tetramethylethylenediaminewere added to a cyclohexane solution containing 35 parts by weight ofstyrene under an atmosphere of nitrogen gas, and polymerization wasconducted at 75° C. for 25 minutes. Thereafter, a cyclohexane solutioncontaining 10 parts by weight of styrene, 10 parts by weight of1,3-butadiene and 7 parts by weight of isoprene was continuously added,and polymerization was conducted at 75° C. for 45 minutes. Then, acyclohexane solution containing 38 parts by weight of styrene wascontinuously added, and polymerization was conducted at 75° C. for 25minutes.

<High Molecular Weight Block Copolymer Moiety>

Using an autoclave equipped with a stirrer, 0.043 part by weight ofn-butyllithium and 0.03 part by weight of tetramethylethylenediaminewere added to a cyclohexane solution containing 35 parts by weight ofstyrene under an atmosphere of nitrogen gas, and polymerization wasconducted at 75° C. for 25 minutes. Thereafter, a cyclohexane solutioncontaining 10 parts by weight of styrene, 10 parts by weight of1,3-butadiene and 7 parts by weight of isoprene was continuously added,and polymerization was conducted at 75° C. for 45 minutes. Then, acyclohexane solution containing 38 parts by weight of styrene wascontinuously added, and polymerization was conducted at 75° C. for 25minutes.

Polymerization solutions of the above-mentioned low molecular weightblock copolymer moiety and high molecular weight block copolymer moietywere mixed at a weight ratio of 50/50. Thereafter, methanol was added inan amount of 0.9 time the molar quality of n-butyllithium to stop thepolymerization, and2-t-amyl-6-[1-(3,5-di-t-amyl-2-hydroxyphenyl)ethyl]-4-t-amylphenylacrylate was added as a stabilizer in an amount of 0.6 part by weightper 100 parts by weight of the block copolymer composition, followed bydesolvation to obtain block copolymer C-1.

9) Block Copolymers C-2 to C-9 and D-1

Block copolymers C-2 to C-9 and D-1 were prepared in a similar manner aswith C-1.

(Preparation of Aliphatic Unsaturated Carboxylic Acid Ester-StyreneCopolymer)

Styrene-n-butyl acrylate copolymers B-1, B-2 and D-2 and styrene-methylmethacrylate copolymer D-3 were produced by adding 5 kg of styrene andn-butyl acrylate or methyl methacrylate at a ratio shown in Table 2 andTable 7 to a 10-liter autoclave equipped with a stirrer, concurrentlyputting 0.3 kg of ethylbenzene and 1 kg of1,1-bis(t-butylperoxy)cyclohexane for adjusting the MRF, conductingpolymerization at 110 to 150° C. for 2 to 10 hours, and then, recoveringunreacted styrene, n-butyl acrylate, methyl methacrylate and ethylbenzene with a vent extruder. B-1 thus obtained had an MRF of 3.0 g/10min, B-2 had an MRF of 2.6 g/10 min, D-2 had an MRF of 3.4 g/10 min, andD-2 had an MRF of 3.1 g/10 min.

(Methods for Measurement and Evaluation)

Measurement and evaluation described in Examples and ComparativeExamples were made by the following methods:

1) Styrene Content

The styrene content of a block copolymer or a hydrogenated blockcopolymer was measured using an ultraviolet spectrophotometer (devicename: UV-2450; manufactured by Shimadzu Corporation.

2) Block Styrene Content and Block Rate

The block styrene content was measured by a method of subjecting a blockcopolymer before hydrogenation to oxidative degradation using t-butylhydroperoxide in the presence of osmium tetraoxide as a catalyst (amethod described in I. M. KOLTHOFF, et al., J. Polym. Sci., 1, 429(1946)). Further, the block rate was determined from the followingequation, using vinyl aromatic hydrocarbon polymer block components(except for vinyl aromatic hydrocarbon polymer block components havingan average polymerization degree of about 30 or less) obtained by themethod.Block rate (% by weight)=(the weight of vinyl aromatic hydrocarbonpolymer blocks in a block copolymer/the weight of the whole vinylaromatic hydrocarbons in the block copolymer)×1003) Block Styrene Peak Molecular Weight

The block styrene peak molecular weight was measured with a GPCapparatus (manufactured by Waters Corporation, U.S.A.) at a sampleconcentration of about 0.05 part by weight at 42° C., using as a samplethe vinyl aromatic hydrocarbon polymer block component obtained in 2),and tetrahydrofuran as a solvent. Phenogel 10⁴, 10⁵ and 10⁶ manufacturedby Phenomenex Inc. were used as columns. Monodisperse polystyrene forGPC was subjected to GPC measurement, and the peak molecular weight wasread from a chromatochart measured, based on calibration curves of thepeak count number thereof and the number average molecular weight of themonodisperse polystyrene.

4) The Amount of Block Styrene of 35000 or Less

The total area of a molecular weight distribution curve was determinedfrom the chromatochart obtained in 3), and a value obtained by dividingan area of a molecular weight of 35000 or less by the total area of themolecular weight distribution curve was represented in percentage.

5) Short-Chain Styrene Content

The content of short-chain styrene polymer moieties contained in a blockcopolymer was obtained by passing oxygen having an ozone (O3)concentration of 1.5% through a dichloromethane solution of the blockcopolymer at 150 ml/min to conduct oxidative degradation, addingdropwise the resulting ozonide into diethyl ether mixed with aluminumlithium hydride to reduce it, then, adding dropwise pure water toconduct hydrolysis, conducting GPC measurement of vinyl aromatichydrocarbon components obtained by adding potassium carbonate to performsalt precipitation and filtration, and calculating the area ratio ofpeaks obtained (see Takayuki Tanaka, Toshiya Sato and YasunobuNakafutami, Kobunshi Gakkai Yokoshu (Preprints of Meeting of the Societyof Polymer Science), 29, 2051 (1980)).

6) Number Average Molecular Weight

The number average molecular weight of a block copolymer or ahydrogenated block copolymer was measured in the same manner as with 3)described above. As for the number average molecular weight,monodisperse polystyrene for GPC was subjected to GPC, and the numberaverage molecular weight was determined according to a conventionalmethod, based on calibration curves of the peak count number thereof andthe number average molecular weight of the monodisperse polystyrene.

7) Amount of Vinyl Bonds and Hydrogenation Ratio

Measurement was made with a nuclear magnetic resonance apparatus(apparatus name: DPX-400; manufactured by Bruker, Germany), using ablock copolymer or a hydrogenated block copolymer.

8) Crystallization Peak and Heat Quantity of Crystallization Peak

The crystallization peak and heat quantity of crystallization peak of ahydrogenated product of a block copolymer were measured with a DSC(apparatus name: DSC 3200S; manufactured by MacScience Co., Ltd.). Thetemperature was elevated from room temperature to 150° C. at atemperature elevation rate of 30° C./min, and then, decreased to −100°C. at a temperature decreasing rate of 10° C./min to measure acrystallization curve, thereby confirming the presence or absence of thecrystallization peak. Further, when the crystallization peak existed,the temperature at which the peak appeared was taken as thecrystallization peak temperature, and the heat quantity ofcrystallization peak was measured.

9) Measurement of Dynamic Viscoelasticity

The dynamic viscoelasticity measurement of a block copolymer or ahydrogenated block copolymer was measured with a viscoelasticitymeasuring apparatus, DVE-V4, manufactured by Rheology Co., Ltd., at anoscillation frequency of 35 Hz at a temperature elevation rate of 3°C./min at a measurement temperature ranging from −100° C. to 150° C.,using as a sample a 2-mm thick test piece obtained by hot presscompression molding. The hot press compression molding was conducted ata temperature of 200° C. under a pressure of 150 Kg/cm² for acompression time of 5 minutes.

10) Shrinkage Ratio

A stretched film was immersed in silicone oil of 65° C. for 5 minutes,and the shrinkage ratio at 65° C. was calculated according to thefollowing equation:Heat shrinkage ratio (%)=(L−L1)/L×100

-   -   L: length before shrinkage,    -   L1: length after shrinkage

Further, a heat shrinkable multilayer film was immersed in hot water of80° C. for 10 seconds, and the shrinkage ratio thereof at 80° C. wascalculated according to the following equation.

11) Natural Shrinkage Ratio

A stretched film having a shrinkage ratio measured at 80° C. of 40% wasallowed to stand at 35° C. for 5 days, and the natural shrinkage ratiois a value calculated according to the following equation:Natural shrinkage ratio (%)=(L2−L3)/L2×100

-   -   L2: length before shrinkage,    -   L3: length after shrinkage

Lower natural shrinkage ratio results in more excellent naturalshrinkability.

Further, a heat shrinkable multilayer film having a shrinkage ratio at80° C. of 30% was allowed to stand at 35° C. for 5 days, and the naturalshrinkage ratio at 80° C. was calculated according to the followingequation.

12) Tensile Elastic Modulus and Breaking Elongation

Measurement was made at a pulling rate of 5 mm/min in the stretchingdirection of a film, based on JIS K-6732. The width of a test piece was12.7 mm, and the distance between gauge marks was 50 mm. Measurement wasmade at a measuring temperature of 23° C. The unit is Kg/cm².

13) Puncture Impact Strength

Measurement was made based on JIS P-8134. The unit is Kg·cm.

14) Haze

A surface of a sheet before stretching was coated with liquid paraffin,and measurement was made based on ASTM D1003.

15) Blocking Property

Two 5-cm×5-cm heat shrinkable multilayer films were superposed upon eachother, and allowed to stand at 40° C. for 7 days with a load of 100g/cm² applied. Then, a blocking state of the films was visually judged.

<Criteria of Judgment>

-   -   A: No blocking is observed.    -   B: Blocking is observed.        16) Fusion Bonding in Hot Water

Stretched films were each wrapped around glass bottles having a diameterof about 8 cm, respectively, and allowed to stand in hot water at 70° C.for 5 minutes in the stacking form of three straw bags. The criteria ofjudgment are as follows:

-   -   S: The films are not fusion bonded at all.    -   A: The films are slightly fusion bonded, but easily separable.    -   B: The films are fusion bonded, and not easily separable.        17) FE

Block copolymer (I) was continuously sheet formed to a sheet having athickness of 0.3 mm, using a 40-mm sheet extruder under conditions of anextrusion temperature of 240° C. for 6 hours. The number of FE's havinga size of 0.5 mm or more per a sheet area of 300 m² after 5 minutes fromthe start of operation and that after 6 hours therefrom were eachcounted, and evaluation was made by the difference in the number of FE'stherebetween.

Examples 1 to 11 and Comparative Examples 1 and 2

In the measurement of the heat shrinkable film performances, acomposition in which the kind and amount of block copolymers: A-1 toA-11, other block copolymers: B-4 (styrene-butadiene-based blockcopolymer, Tufprene 126 manufactured by Asahi Chemical Industry Co.,Ltd.) and B-5 (styrene-butadiene-based hydrogenated block copolymer,Tuftec 1041 manufactured by Asahi Chemical Industry Co., Ltd.),styrene-n-butyl acrylate copolymers: B-1 and B-2, and general-purposepolystyrene: B-3 (A&M Polystyrene 685 manufactured by A&M Styrene Co.Ltd.) are shown in Table 4 was molded to a sheet form having a thicknessof 0.25 mm at 200° C., using a 40-mm extruder, and then, the sheet wasuniaxially stretched at a stretching ratio of 5 at a stretchingtemperature of 100° C. (in Comparative Example 5, stretching at 100° C.was impossible, so that the sheet was stretched at 110° C.) in thetransverse direction, using a tenter, thereby obtaining a heatshrinkable film having a thickness of about 60 μm. The film performancesof this heat shrinkable film are shown in Table 4. It is seen that theperformances of the heat shrinkable films of the invention are excellentin rigidity represented by tensile elastic modulus, low-temperatureshrinkability represented by the heat shrinkage ratio at 65° C., naturalshrinkability, impact resistance represented by puncture impactstrength, fusion bonding in hot water, and transparency represented byhaze. The sheet and film performances were conducted by theabove-mentioned methods.

Examples 12 to 19 and Comparative Examples 3 to 6

Compounded compositions shown in Table 9 were extruded through a T-dieto form a three-layer sheet using the compositions as an intermediatelayer and surface and back layers, and the sheet was longitudinallystretched 1.2 times to form a sheet having a thickness of 0.25 mm. Then,the sheet was laterally stretched 5 times with a tenter to obtain a heatshrinkable film having a thickness of about 50 μm. The thickness ratio(%) of the intermediate layer and the surface and back layers was 15(surface layer)/70 (intermediate layer)/15 (back layer). Theperformances of the resulting three-layer heat shrinkable films areshown in Table 9. Adekastab LA-32 (manufactured by Asahi Denka Co.,Ltd.) was added as an ultraviolet absorber in an amount of 0.2 part byweight per 100 parts by weight of the surface and back layers. Styrenepolymers, aliphatic unsaturated carboxylic acid ester-styrene copolymersand rubber-modified styrene polymers are shown in Table 7, andlubricants are shown in Table 8. The sheet and film performances wereconducted by the above-mentioned methods. TABLE 1 Amount of Block PeakMolecular Styrene of 35000 or Styrene Content Butadiene/Isoprene NumberAverage Block Rate Weight of Block Less (% by weight) (weight ratio)Molecular Weight (% by weight) Styrene (% by weight) A-1 80 100/0 148000 52 (1) 12000 63 (2) 70000 A-2 74 50/50 132000 55 (1) 9000 67 (2)42000 A-3 72 30/70 128000 57 (1) 9000 71 (2) 50000 A-4 58 100/0  1200008 (1) 8500 76 (2) 28000 A-5 93 50/50 187000 86 (1) 13000 12 (2) 170000

TABLE 2 Amount of 35000 or Less of Styrene Number Block Content AverageStyrene Butadiene/ Peak Molecular Block Rate Styrene (% by ComponentMolecular Content Isoprene Weight of Block (% by (% by weight) (% byweight) Weight (% by weight) (weight ratio) Styrene weight) weight) A-679 (Component 1) 163000 87 40/60 (1) 23000 64 49 60 (2) 108000(Component 2) 74000 68 40/60 (1) 12000 40 (2) 43000 A-7 77 (Component 1)163000 87 40/60 (1) 24000 55 63 50 (2) 112000 (Component 3) 80000 6750/50 (1) 22000 50 A-8 78 (Component 4) 172000 90 30/70 (1) 26000 54 6245 (Component 2) 74000 68 40/60 (1) 12000 55 (2) 43000 A-9 70 — 105000 —50/50 (1) 18000 50 74 (2) 38000 A-10 75 — 51000 — 100/0 (1) 12000 73 69(2) 38000 A-11 79 (Component 1) 148000 87 40/60 (1) 19000 67 63 60 (2)96000 (Component 2) 68000 68 40/60 (1) 9500 40 (2) 39000

TABLE 3 Styrene Content (% by weight) B-1 79 B-2 88 B-3 100B-1, 2: Styrene-n-butyl acrylate copolymerB-3: A&M Polystyrene 685 (manufactured by A&M Styrene Co. Ltd.)

TABLE 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Compounding Kind andAmount of Block A-1 A-2 A-3 A-3 A-2 A-6 A-7 Composition Copolymer (A) (%by 100 100 90 80 90 94 96 weight) Kind and Amount of — — B-1 B-2 B-3 B-4B-5 Styrene Resin (B) etc. (% — — 10 20 10 6 4 by weight) Sheet · FilmTensile Elastic Modulus 16800 15800 16800 17300 17100 16300 15800Performances (Kg/cm²) Puncture Impact Strength 11 16 10 9 9 12 12 (Kg ·cm) Haze (%) 0.3 0.4 0.6 0.7 0.8 0.5 0.9 Shrinkage Ratio at 65° C. 24 2926 22 19 23 21 (%) Natural Shrinkage Ratio 0.13 0.09 0.11 0.15 0.23 0.120.15 (%) Fusion Bonding in Hot A A A S S A A Water Ex. 8 Ex. 9 Ex. 10Ex. 11 Com. Ex. 1 Com. Ex. 2 Compounding Kind and Amount of Block A-8A-9 A-10 A-11 A-4 A-5 Composition Copolymer (A) (% by weight) 100 65 100100 100 100 Kind and Amount of Styrene — B-1 — — — — Resin (B) etc. (%by weight) — 35 — — — — Sheet · Film Tensile Elastic Modulus (Kg/cm²)16300 16200 17600 16900 8100 20800 Performances Puncture Impact Strength9 12 13 10 20 or more 2 or more (Kg · cm) Haze (%) 0.3 0.3 0.8 0.6 0.30.3 Shrinkage Ratio at 65° C. (%) 28 33 18 21 40 4 Natural ShrinkageRatio (%) 0.11 0.08 0.17 0.14 1.6 6.2 Fusion Bonding in Hot Water A A SS B SB-4: Tufprene 126 (manufactured by Asahi Chemical Industry Co., Ltd.)B-5: Tuftec 1041 (manufactured by Asahi Chemical Industry Co., Ltd.)

TABLE 5 Polymer Structure Composition Block Copolymer (*1) Ratio C-1Component (A-a) S—B/I/S—S 35-10/10/7-38 Component (A-b) S—B/I/S—S35-10/10/7-38 C-2 Component (A-a) S—B/I/S—S 30-15/8/6-41 Component (A-b)S—B/I/S—S 30-15/8/6-41 C-3 Component (A-a) B/S—S—B/I/S—S 8/5-25-1/6/8-47Component (A-b) S—B/I/S—S 8/5-25-1/6/8-47 C-4 Component (A-a) S—B/I/S—S58-13/8/3-18 Component (A-b) S—B/I/S—S 31-21/14/5-29 C-5 Component (A-a)(S—B/I/S)4-X 70-11/9/10 Component (A-b) (S—B/I/S)4-X 70-11/9/10 C-6Component (A-a) S—B—S 25-45-30 Component (A-b) S—B—S 25-45-30 C-7Component (A-a) S—B/I/S—S 45-1/1/3-50 Component (A-b) S—B/I/S—S45-1/1/3-50 C-8 Component (A-a) S—B/I/S—S 30-12/6/30-22 Component (A-b)S—B/I/S—S 30-12/6/30-22 C-9 Component (A) S—B/I/—S 41-12/6-41 D-1Component (A) S—B/I/S—S 25-20/5/14-36*1 B/I represents a copolymer moiety of butadiene and isoprene, B/I/Srepresents a copolymer moiety of butadiene, isoprene and styrene, Srepresents a styrene moiety, and X represents a residue of silicontetrachloride.2-[1-(2-Hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenylacrylate was added as a stabilizer to all block copolymers in an amountof 0.3 part by weight per 100 parts by weight of the block copolymer.

TABLE 6 C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 C-9 Styrene Content (% byweight) 83 77 85 72 80 55 98 82 82 Butadiene Content (% by weight) 10 159 17 11 45 1 12 12 Isoprene Content (% by weight) 7 8 6 11 9 0 1 6 6Block Styrene Content 73 71 72 68 70 55 95 52 82 (parts by weight)Single-Chain Styrene 10 4 12 3 9 0 2 31 0 Content (% by weight) TanδPeak 118 119 110 109 120 123 127 86 129 Temperature (° C.) PeakMolecular Component (A-a) 160000 140000 190000 170000 140000 93000142000 160000 — Weight of Component (A-b) 70000 90000 65000 46000 7000030000 68000 52000 130000 Block Copolymer Component (A-a)/ 50/50 40/6040/60 45/55 60/40 80/20 60/40 45/55 — Component (A-b) Weight Ratio

TABLE 7 D-1 D-2 D-3 D-4 D-5 Styrene Content (% by weight) 75 82 90 HIPSGPPS Butadiene Content (% by weight) 20 — — Isoprene Content (% byweight) 5 — — Block Styrene Content (parts by weight) 61 — —Single-Chain Styrene Content (% by weight) 7 — — Methyl MethacrylateContent (% by weight) — — 10 n-Butyl Acrylate Content (% by weight) — 18— Structure of Block Copolymer*1 S-B/I/S-S — —HIPS: A&M Polystyrene 475D (manufactured by A&M Styrene Co. Ltd.)GPPS: A&M Polystyrene 685 (manufactured by A&M Styrene Co. Ltd.)The number average molecular weight of block copolymer D-1 is 93000, andthe single-chain styrene content is 16% by weight.

TABLE 8 E-1 Stearoamide E-2 Microcrystalline Wax E-3 Stearic Acid

TABLE 9 Com. Com. Com. Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18Ex. 19 Ex. 3 Ex. 4 Ex. 5 Surface Block Copolymer (% by weight) C-1 C-2C-3 C-4 C-5 C-1 C-3 A-10 C-6 C-7 C-8 Layer · 98 90 98 80 100 95 92 98 8098 90 Back Styrene Resin etc. (% by — D-3 — D-1 — D-7 D-6 — D-2 — D-5Layer weight) 8 18 5 6 18 8 (% by D-4 D-4 D-4 D-4 D-4 D-4 D-4 D-4 D-4D-4 D-4 weight) 2 2 2 2 2 2 2 2 2 2 2 Lubricant (% by weight) E-1 E-1E-1 E-1 E-1 E-2 E-3 E-1 — E-1 E-1 0.2 0.2 0.2 0.2 0.2 0.5 0.5 0.2 0.20.2 Inner Block Copolymer (% by weight) D-1 D-1 D-1 D-1 D-1 D-1 C-4 D-1D-1 D-1 D-1 Layer 60 60 60 60 60 60 50 60 60 60 60 Styrene Resin etc. (%by weight) D-2 D-2 D-2 D-2 D-2 D-2 D-2 D-2 D-2 D-2 D-2 40 40 40 40 40 4050 40 40 40 40 Physical Tensile Elastic Modulus kgf/cm² 16900 1790017700 17100 17400 16600 16400 16300 15400 19600 18300 propertiesElongation at Break % 140 100 110 120 130 170 190 170 220 40 70 PunctureImpact Value kgf-cm 5.2 4.6 4.8 4.9 5.0 5.6 5.7 5.6 6.4 2.4 3.2 HazeValue % 3.2 3.4 3.2 3.2 3.0 3.9 3.6 3.4 7.6 3.1 3.2 Shrinkage Ratio at80° C. % 28 23 26 26 27 27 27 30 29 14 17 Natural Shrinkage Ratio % 1.61.8 1.6 1.7 1.6 1.7 1.8 1.6 1.5 3.3 2.9 Fusion Bonding in Hot Water A AA A A A A A B A B Blocking Property A A A A A A A A B A A FE A A A A A AA A B A AD-6: Tufprene 126 (manufactured by Asahi Chemical Industry Co., Ltd.)D-7: Tuftec 1041 (manufactured by Asahi Chemical Industry Co., Ltd.)

Although the invention has been described in detail and with referenceto specific embodiments thereof, it will be apparent to one skilled inthe art that various changes and modification may be made thereinwithout departing from the spirit and scope of the invention.

This application is based on Japanese patent application Nos.2002-123510 (filed on Apr. 25, 2002), 2002-341185 (filed on Nov. 25,2002) and 2003-026606 (filed on Feb. 4, 2003), the contents thereofbeing incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The heat shrinkable film using the block copolymer or hydrogenated blockcopolymer of the invention is transparent and excellent in rigidity,natural shrinkability, low-temperature shrinkability, fusion bonding inhot water and impact resistance. Accordingly, it can achieve thinning ofthe film, and dimensional stability and low-temperature shrinkability atthe same time, and can be suitably utilized for drink containerpackaging, cap seals, various labels and the like.

Further, the heat shrinkable multilayer film using the block copolymeror hydrogenated block copolymer of the invention has a few FE's, and issatisfactory in natural shrinkability, rigidity, blocking resistance,resistance to fusion bonding in hot water, impact resistance, andfurther, low-temperature shrinkability. Making the best use of thefeature that the film has a few FE's like this, it can be suitablyutilized for various packaging film applications such as labels and capseals on which various prints are applied.

1. A block copolymer having a weight ratio of a vinyl aromatichydrocarbon and a conjugated diene of 60/40 to 90/10 and a numberaverage molecular weight measured by gel permeation chromatography (GPC)of 30,000 to 500,000, wherein the vinyl aromatic hydrocarbonconstituting the block copolymer has a block rate of from 10 to 90% byweight, the vinyl aromatic hydrocarbon polymer blocks constituting theblock copolymer have a peak molecular weight within the molecular weightrange of 5,000 to 30,000, and 40 to 80% by weight of the vinyl aromatichydrocarbon polymer blocks have a molecular weight of 35,000 or less. 2.The block copolymer according to claim 1, wherein the vinyl aromatichydrocarbon polymer blocks have peak molecular weights within themolecular weight range of 5,000 to 30,000 and within the molecularweight range of 35,000 to 150,000, respectively.
 3. The block copolymeraccording to claim 1 or 2, which comprises: 10 to 90 parts by weight ofa block copolymer (component 1) having a weight ratio of a vinylaromatic hydrocarbon and a conjugated diene constituting the blockcopolymer of from 70/30 to 95/5, wherein the vinyl aromatic hydrocarbonpolymer blocks have peak molecular weights within the molecular weightrange of 5,000 to 30,000, and within the molecular weight range of35,000 to 150,000, respectively; and 90 to 10 parts by weight of a blockcopolymer (component 2) having a weight ratio of a vinyl aromatichydrocarbon and a conjugated diene constituting the block copolymer offrom 50/50 to 85/15, wherein the vinyl aromatic hydrocarbon polymerblocks have peak molecular weights within the molecular weight range of5,000 to 30,000, and within the molecular weight range of 35,000 to150,000, respectively, with the proviso that the total amount ofcomponent 1 and component 2 is 100 parts by weight, and that component 1has a vinyl aromatic hydrocarbon content larger than that of component 2by at least 3% by weight.
 4. The block copolymer according to claim 1 or2, which comprises: 10 to 90 parts by weight of a block copolymer(component 1) having a weight ratio of a vinyl aromatic hydrocarbon anda conjugated diene constituting the block copolymer of from 70/30 to95/5, wherein the vinyl aromatic hydrocarbon polymer blocks have peakmolecular weights within the molecular weight range of 5,000 to 30,000,and within the molecular weight range of 35,000 to 150,000,respectively; and 90 to 10 parts by weight of a block copolymer(component 3) having a weight ratio of a vinyl aromatic hydrocarbon anda conjugated diene constituting the block copolymer of from 50/50 to85/15, wherein the vinyl aromatic hydrocarbon polymer blocks have a peakmolecular weight within the molecular weight range of 5,000 to 30,000,with the proviso that the total amount of component 1 and component 3 is100 parts by weight, and that component 1 has a vinyl aromatichydrocarbon content larger than that of component 3 by at least 3% byweight.
 5. The block copolymer according to claim 1 or 2, whichcomprises: 10 to 90 parts by weight of a block copolymer (component 4)having a weight ratio of a vinyl aromatic hydrocarbon and a conjugateddiene constituting the block copolymer of from 70/30 to 95/5, whereinthe vinyl aromatic hydrocarbon polymer blocks have a peak molecularweight within the molecular weight range of 5,000 to 30,000; and 90 to10 parts by weight of a block copolymer (component 2) having a weightratio of a vinyl aromatic hydrocarbon and a conjugated dieneconstituting the block copolymer of from 50/50 to 85/15, wherein thevinyl aromatic hydrocarbon polymer blocks have peak molecular weightswithin the molecular weight range of 5,000 to 30,000, and within themolecular weight range of 35,000 to 150,000, respectively, with theproviso that the total amount of component 4 and component 2 is 100parts by weight, and that component 4 has a vinyl aromatic hydrocarboncontent larger than that of component 2 by at least 3% by weight.
 6. Theblock copolymer according to claim 1 or 2, having a content ofshort-chain vinyl aromatic hydrocarbon polymer moieties with a vinylaromatic hydrocarbon unit number of 1 to 3, of from 1 to 25% by weightbased on the total amount of the vinyl aromatic hydrocarbonsconstituting the block copolymer.
 7. The block copolymer according toclaim 1 or 2, wherein the conjugated diene constituting the blockcopolymer comprises butadiene and isoprene, and the weight ratio ofbutadiene and isoprene in the block copolymer is within the range of3/97 to 90/10.
 8. The block copolymer according to claim 1 or 2, whereinat least one polymer block selected from the group consisting of (i) acopolymer block comprising isoprene and 1,3-butadiene, (ii) a copolymerblock comprising isoprene and a vinyl aromatic hydrocarbon and (iii) acopolymer block comprising isoprene, 1,3-butadiene and a vinyl aromatichydrocarbon is incorporated into the block copolymer.
 9. A hydrogenatedblock copolymer obtained by hydrogenating the block copolymer accordingto claim 1 or
 2. 10. The hydrogenated block copolymer according to claim9, which has a crystallization peak in a temperature region of 20° C. orhigher, in a differential scanning calorimetry (DSC) chart.
 11. A blockcopolymer composition comprising: component (A) which is the blockcopolymer according to claim 1 or 2 or a hydrogenated product thereof;and component (B) which is a vinyl aromatic hydrocarbon polymer, whereinthe weight ratio of component (A) and component (B) is from 99.9/0.1 to20/80.
 12. The block copolymer composition according to claim 11,wherein the vinyl aromatic hydrocarbon polymer of component (B) is atleast one member selected from the group consisting of the following a)to c): a) styrene polymers b) aliphatic unsaturated carboxylic acidester-styrene copolymers, and c) rubber-modified styrene polymers. 13.The block copolymer composition according to claim 11, which contains atleast one lubricant selected from the group consisting of fatty acidamides, paraffins, hydrocarbon resins, and fatty acids in an amount of0.01 to 5 parts by weight per 100 parts by weight of the block copolymeror hydrogenated product thereof.
 14. The block copolymer compositionaccording to claim 11, which contains at least one stabilizer selectedfrom the group consisting of2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenylacrylate,2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methyl-phenylacrylate and 2,4-bis[(octylthio)methyl]-o-cresol in an amount of 0.05 to3 parts by weight per 100 parts by weight of the block copolymer orhydrogenated product thereof.
 15. The block copolymer compositionaccording to claim 11, which contains at least one ultraviolet absorberor light stabilizer selected from the group consisting ofbenzophenone-based ultraviolet absorbers, benzotriazole-basedultraviolet absorbers and hindered amine-based light stabilizers in anamount of 0.05 to 3 parts by weight per 100 parts by weight of the blockcopolymer or hydrogenated product thereof.
 16. A sheet/film comprisingthe block copolymer or hydrogenated product thereof, or the blockcopolymer composition according to any one of claims 1 to
 15. 17. A heatshrinkable film obtained by stretching the film comprising the blockcopolymer or hydrogenated product thereof, or the block copolymercomposition according to any one of claims 1 to 15, wherein the film hasa heat shrinkage ratio at 65° C. in the stretching direction of from 5to 60%, and a tensile elastic modulus in the stretching direction of7,000 to 30,000 Kg/cm².
 18. A heat shrinkable multilayer film comprisingas at least one layer of the multilayer film a layer obtained bystretching a film comprising the block copolymer or hydrogenated productthereof, or the block copolymer composition according to any one ofclaims 1 to 15, wherein the heat shrinkage ratio at 80° C. in thestretching direction is from 10 to 80%.
 19. A heat shrinkable multilayerfilm comprising as at least one layer of the multilayer film a layercomprising the block copolymer or hydrogenated product thereof, or theblock copolymer composition according to any one of claims 1 to 15,which has at least two peak molecular weights within the range of 40,000to 300,000, in the gel permeation chromatography (GPC) measurement, andmoreover, has at least one tan δ peak temperature within the temperaturerange of 90 to 125° C., in the dynamic viscoelasticity measurement. 20.The heat shrinkable multilayer film according to claim 18 or 19, havinga heat shrinkage ratio at 65° C. in a stretching direction of from 5 to60%, and a tensile elastic modulus in a stretching direction of 7,000 to30,000 Kg/cm².